There are explosion-proofing mechanisms known in the related art that cut off an electric current flowing to a sealed secondary battery when it becomes overcharged resulting in an increase in the internal pressure, so as to prevent a further rise in the internal pressure. PTL1, for instance, discloses an explosion-proofing mechanism having a diaphragm that inverts when there is a rise in the internal pressure so as to break the connection inside the battery and thus cut off the electric current.